1. Field of the Invention
The present invention relates to a map database apparatus which, preferably mounted in a navigation system for vehicles and the like, is used in road map display, map matching, calculation of a recommended route and the like.
2. Description of the Prior Art
Vehicular navigation systems in the known art are provided with a function for displaying a road map of the area where the vehicle is currently located, a function for accurately detecting the vehicle position through map matching, a function for calculating a recommended route from a point of departure to a destination and the like. In these vehicular navigation systems in the prior art, data for road map display, data for map matching and data for route search are separately stored in a storage medium in order to maintain compatibility with existing software programs and also to improve the processing speed.
This means that a large storage capacity is required and, even with CD ROM as the storage medium, it has become difficult to store road map data for the entire nation of Japan on one CD ROM disk. However, if data are stored on a plurality of CD ROM disks, the CD ROM disks will have to be replaced during use, reducing the operability. If, on the other hand, a CD ROM device employing the auto-changer system is used, whereby a plurality of CD ROM disks are automatically changed, the product cost will increase.
FIG. 23 shows the data management method for road map data in the navigation system in the prior art. As shown in the figure, data are managed in units of links which are the minimum unit required for expressing road physical forms and, for each link, node information related to the nodes at both ends of the link is provided. In addition, even though nodes have identical positional coordinates, the nodes are managed with different node nos. for individual links. Information that indicates that adjacent nodes of adjacent links have the same positional coordinates (hereafter referred to as identical node information) is provided separately. For instance, in FIG. 23, information C12 and C21 are provided, which indicate that node N1b of link L1 and node N2a of link L2 are equal to each other.
FIG. 24 shows the range of an intersection where a plurality of roads intersect. In a case such as that presented in FIG. 24, in the prior art, each road is divided at the intersection being the boundary into separate links respectively, as shown in FIG. 25, and separate nodes are assigned to the intersection for each road. In addition, identical node information, which indicates that nodes N0a, N0b, N0c,N0d and N0e have the same positional coordinates, is provided separately.
Since the identical node information described above must be provided at each location where links are connected, many sets of identical node information are required for the entire road map. Thus, a large quantity of data is required for the identical node information alone, and this is a significant factor in the increase in storage capacity requirement of the storage medium, such as CD ROM.